I will be travelling with a colleague, who will be encouraged to carry one of my other Pentax DSLRs (KP or K-1) and a couple of extra lenses, so backup is taken care of. Maybe I should throw my LX and a couple of old lenses (my FA20, FA31, A50/1.2 or FA77 come to mind) in my checked luggage as well....

As an occasional mountaineer and cross-country skier, I have plenty of clothing for cold weather. I have tried and failed to grow a decent beard in the past, but will not be packing a shaver for the trip

Dress in layers and keep your batteries warm - as close to you as possible, and bring lots. You will eat through batteries very fast in the cold. Bring warm socks, gloves and hats that cover your ears. No sense in bringing frostbite home.

Traveled to an Inuvialuit whaling camp 350 miles North of the Arctic Circle during the warm season. The frozen line of the permanent ice shelf was visible from camp. I think you'll be fine. I didn't even have to worry about battery power in the seasonal warmth. But you may be much closer to the pole?

As long as you have a second body, your kit is more than sufficient. On Alaska and NW Territory trips, I tended to cut back even more than that, but also carried 67 as my primary kit with 35mm backup. I've always been a Pelicase guy for excursions and boats and run them with individually bagged lenses (just standard Pentax pouches) so I don't waste space on the foam interior (I keep the lid foam in place and the thin foam on the bottom. I keep 5 different sizes and fit the "kit of the day" to the right size Pelican). The gear packs together quite solidly and carries like a briefcase...more field-ready than you might think. Set it down anywhere you want...closed lid works great as a board for cutting cheese and bread etc. Tripod over one shoulder with kit case in the other hand for balance. Works fabulous for walks up to a mile...cumbersome for longer. But way easier to work from than most soft packs (no issues with dirt, mud, moisture. Pack straps are notorious when you set the pack on the ground with straps down--every time). Pelican-cased the Pentax 67II kit, Hassy XPanII kit and for 3 decades now with all the Pentax 35mm and APS kits.

Remember you will be in a marine environment--even when onshore--which will quickly reduce your number of lens changes and number of lenses you really use. The salt air tends to become almost greasy just from invisible mist depositing it. (Salt and magnesium camera don't mix! Magnesium is hyper corrosive. Keep your hands/gloves clean and carry hand towels to wipe surfaces).

I always found the 80-200 to end up being a workhorse when shooting from a boat at things outside the boat. When the action is inside the boat the 24-70 range is highly applicable...so I have tended toward the two lenses you've rejected. But hey, the other options didn't exist when I was traveling 150 days a year.

Also, took a couple trips to Yellowknife NWT without any macro lens. Took one of the multi-element achromat screw-in adapters...the 77mm Canon 500D works really well on 80-200 and also on various 300mm lenses, though I've never tried it on the DA*300. It gives me very sufficient half-lifesize macro with more than passable sharpness. If the likelihood of shooting really tight macro is not that great, you could save space this way, but if you don't take the 80-200 that leaves you with the 300 as your macro.

For many summer trips up North, the mesh bug jacket was a necessary accessory. Don't know what shore will be like on "the continent" but you might want to ask.

K-1 and KP (I could even swap the KP for my old K-3, which currently lives with my brother, to share the better battery of the K-1)
Samyang fisheye
DFA15-30
DFA24-70 (if I have the 100 macro anyway, this might make more sense than the DFA28-105)
DA*55
DFA100WR
HD DA55-300 +/- 1.4xTC (lose some IQ at the long end, but gain the versatility of a zoom, shared 58mm filters, and on the KP or K-3, more pixels at the same reach)

Without the DA*300 it's the same total weight, even with the spare body.

In an ideal world of course I'd take my other K-1 and buy a DFA150-450, but that would blow my weight limit (and budget!).

I'm off to Antarctica next December, with a couple of days each way on an ice-breaker and some time in Argentina either side. The ship is The National Geographic Explorer, which will populated by scientists, explorers and professional photographers as well as us our group. . . .

I agree on using the K3 to maximize battery sharing ability or use of one type of battery. I did not see it in the list, but a portable back up drive that accepts SD cards would be useful. I took one on my trip, a Passport wireless, it was lightweight, and about the same size as a paperback book.